How big is the bit of dust that makes a shooting star?
Usually tiny: most shooting stars are made by grains between the size of a grain of sand and a small pea.
It is amazing, but most shooting stars are made by pieces of space dust smaller than a pea. Many are only the size of a grain of sand.
How can something so small make such a bright flash? The secret is speed. These tiny grains hit Earth's air at between 11 and 72 kilometres every second. At that speed, even a speck carries a lot of energy, like a tiny bullet. When it slams into the air, it heats the air around it to thousands of degrees, making it glow brightly enough to be seen from far below.
Here is a rough guide:
- A grain the size of a grain of sand makes a faint shooting star, the kind you see on a dark night. - A grain the size of a pea can make a bright shooting star, brighter than most stars. - A pebble the size of a marble or grape can make a very bright fireball. - A rock the size of a football or bigger can make a dazzling fireball, and sometimes pieces reach the ground as meteorites.
Because shooting stars are made by such tiny grains, they burn up completely, high above the ground. That is why you never need to worry about being hit by a shooting star during a meteor shower.